The present invention concerns an exterior element for the middle part of a timepiece case such as a timepiece bezel.
Exterior elements such as known rotating bezel systems 2, seen in FIG. 1, comprise a rotating bezel 4 taking the form of an annular part. This annular part has a top face and a bottom face, the top face being the face seen by the user. As seen in FIG. 2, this bezel 8 has a toothing 10 in the bottom surface thereof. The rotating bezel system further includes a spring means 11. This spring means 11 is inserted between the rotating bezel and the middle part 3 of timepiece 1, when bezel 4 is forcibly fitted onto the middle part of the timepiece. This spring means 11 takes the form of a flat ring comprising leaves on the surface thereof facing the toothing in bezel 8. These leaves are arranged to tilt relative to the plane of the flat ring. The leaves have some elasticity so that the spring means acts on the rotating bezel to exert a vertical force. This vertical force has a tendency to push the bezel off the middle part of the timepiece.
The leaves also serve to cooperate with the toothing in the bezel. The leaves and toothing are then configured so that the bezel can only rotate in one direction, since the leaves prevent the bezel from rotating if the user attempts to rotate said bezel in the wrong direction. Generally, the bezel and the spring means are made of steel which has the advantage of being durable and inexpensive.
The bezel is driven onto the middle part 2 of the watch case. To achieve this, the middle part has a peripheral shoulder 2a in which said rotating bezel system is placed. The shoulder 2a has a wall 2b parallel to the central axis (C) of the middle part and a wall perpendicular to the central axis of the middle part. Parallel wall 2b of said shoulder has a peripheral groove 2c. Bezel 8 is an annular part having a peripheral rim 8a on the bottom face thereof. The rim is provided with a continuous addendum 12 extending along said rim towards the axial centre of the bezel. When said rotating bezel system is driven onto the middle part of the watch case, the continuous addendum is inserted into the peripheral groove of the shoulder ensuring that the bezel is held vertically on the middle part.
One drawback of this system is that it cannot be disassembled. Indeed, the bezel of prior art rotating bezel systems is driven onto the middle part of the case so that any attempt to remove the rotating bezel system generally has to be achieved by pulling the system off, which results in its destruction.
Naturally, this depends on the material of which the bezel is made. A plastic bezel which is driven onto the middle part will be easier to remove than a steel bezel. This tendency arises from the fact that plastic has elastic properties meaning that it deforms more easily than steel, which means that it is easier to assemble and disassemble a plastic bezel than a steel bezel.